101. The Comma.—As we have seen, the period is used to close a declarative sentence, and the semicolon and colon are used to mark off the greater divisions of a sentence. The office of the comma is to point off the smaller divisions of a sentence. It is used in the following ways:—
1. In a compound sentence, to separate the different clauses, when there is not a sufficient break in the thought to make the semicolon necessary. See above, §99, 1.
He rested himself in the Chancellor's room till the debate commenced, and then, leaning on his two relatives, he limped to his seat.
His exertions redeemed his own fame, but they effected little for his country.
2. To separate the different parts of a compound predicate, unless the connection between them is very close.
The slightest particulars of that day were remembered, and have been carefully recorded.
He lost the thread of his discourse, hesitated, repeated the same words several times, and was so confused that, in speaking of the Act of Settlement, he could not recall the name of the Electress Sophia.
I see and hear you.
3. In a complex sentence in which the dependent clause precedes, to separate the dependent clause from the principal clause. When the dependent clause follows, the comma is, as a rule, not needed.
If you are wise, you will trust him implicitly.
Although I saw him, I could not wait.
I would not stop until he called out to me.
4. To mark off an explanatory relative clause.
Note.—Relative clauses may be roughly divided into explanatory clauses and restrictive clauses. An explanatory relative clause describes or gives information about its antecedents. A restrictive relative clause narrows the meaning of its antecedent. An explanatory clause might usually be omitted without affecting the thought of the principal clause. A restrictive clause cannot usually be omitted without affecting the thought of the principal clause. No comma is used before a restrictive clause.
Examples. (a) Explanatory Clauses.—1. The twenty-four columns, each of which is sixty feet in height, are oppressive in their grandeur.
2. Beyond lay various other apartments, which receive no light from without.
3. This churchman rode upon a well-fed, ambling mule, whose bridle was ornamented with silver bells.
4. His companion, who was a man past forty, was tall and muscular.
(b) Restrictive Clauses.—1. The two who rode foremost were persons of importance.
2. This is not the book that I ordered.
3. There is no reason which can be urged in favor of such a bill.
4. Such was the appearance of the man who was about to receive into his hand the destinies of half the world.
5. We walked through the inner halls under the spell of a fascination which we had hardly power to break.
5. In general, to indicate the beginning and the end of a group of words, whether a phrase or a clause, which must be regarded as a unit, particularly if it occurs parenthetically.